1. Field of the Invention
The present invention generally relates to a rotation direction detection apparatus. More specifically, the present invention relates to a rotation direction detection apparatus that detects the direction of rotation of a rotating body that is rotatably mounted to a fixed unit. The present invention is especially suitable for a rear derailleur.
2. Background Information
In order to permit the gear shifting operation on a bicycle to be carried out using little effort, electric-powered gear shift mechanisms that carry out gear shifting for a bicycle using an actuator have been developed in recent years. When an external gear shift mechanism is used, because gear shifting is carried out by disengaging a chain from one of a plurality of gears, gear shifting cannot be carried out if the chain is not rotating in the forward direction, i.e., if the pedals are not being pushed in the direction of forward motion. As a result, in order to make the gear shifting operation of the external gear shift mechanism electric-powered, a rotation direction detection apparatus that can detect whether or not the pedals are being pushed in the direction of forward motion is necessary.
This type of rotation direction detection apparatus typically includes a detection element consisting of a magnet, for example, that is fixed to the bicycle cranks and a pair of reed switches that alternate between the “ON” and “OFF” states by detecting the magnetic force of the detection element. The reed switches are arranged side by side in the direction of rotation. The direction of crank rotation, which determines whether or not the pedals are being pushed in the direction of forward motion, is detected by determining which of the pair of magnets arranged in the direction of rotation turns “ON” or “OFF” first.
With the conventional rotation direction detection apparatus described above, because the direction of rotation is detected using a pair of reed switches, the construction of the apparatus becomes complex, as does the processing performed in order to detect such direction. Furthermore, because the two reed switches must be disposed with a distance therebetween in the direction of rotation, it is difficult to keep the apparatus compact in size.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved rotation direction detection apparatus. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.